The parasympathetic tone activity (PTA) index is based on heart rate variability and has been developed recently in animals to assess their relative parasympathetic tone. This study aimed to evaluate PTA index in anaesthetized horses with different health conditions and the performance of PTA variations (∆PTA) to predict changes in mean arterial pressure (MAP).

Thirty-nine client-horses were anaesthetized for elective or colic surgery and divided into “Elective” and “Colic” groups. During anaesthesia, dobutamine was administered as treatment of hypotension (MAP <60 mmHg).

In both groups, no significant variation of PTA and MAP were detected immediately before and after cutaneous incision. The PTA index increased 5 min before each hypotension, whereas it decreased 1 min after dobutamine administration. Horses of the Colic group had lower PTA values than those of the Elective group, whereas MAP did not differ between groups. To predict a 10% decrease in MAP, ΔPTA performance was associated with: AUC ROC [95% CI] =0.80 [0.73 to 0.85] (p < 0.0001), with a sensitivity of 62.5% and a specificity of 94.6% for a threshold value of 25%.

The PTA index in anaesthetized horses appears to be influenced by the health condition. The shift toward lower PTA values in colic horses may reflect a sympathetic predominance. An increase in PTA of >25% in 1 min showed an acceptable performance to predict MAP decrease of >10% within 5 min. Even though these results require further evaluation, this index may thus help to predict potential autonomic dysfunctions in sick animals.

副交感神经张力活动 (PTA) 指数基于心率变异性，最近已在动物身上开发，以评估它们的相对副交感神经张力。本研究旨在评估具有不同健康状况的麻醉马匹的 PTA 指数以及 PTA 变化 (ΔPTA) 的性能，以预测平均动脉压 (MAP) 的变化。

三十九匹客户马被麻醉以进行选择性或绞痛手术，并分为“选择性”和“绞痛”组。在麻醉期间，多巴酚丁胺用于治疗低血压（MAP <60 mmHg）。

在两组中，在皮肤切口前后即刻没有检测到 PTA 和 MAP 的显着变化。PTA 指数在每次低血压前 5 分钟增加，而在多巴酚丁胺给药后 1 分钟下降。绞痛组的马匹的 PTA 值低于选修组的马匹，而各组之间的 MAP 没有差异。为了预测 MAP 降低 10%，ΔPTA 性能与：AUC ROC [95% CI] =0.80 [0.73 至 0.85] ( p  < 0.0001)，阈值的敏感性为 62.5%，特异性为 94.6% 25% 的价值。

麻醉马匹的 PTA 指数似乎受健康状况的影响。绞痛马向较低 PTA 值的转变可能反映了交感神经的优势。1 分钟内 PTA 增加 >25% 表明预测 5 分钟内 MAP 下降 >10% 的性能是可以接受的。尽管这些结果需要进一步评估，但该指数可能因此有助于预测患病动物的潜在自主神经功能障碍。